With the development of various high-radiance light sources, in particular the universal application of light emitting diode (LED) in indication, display and lighting, the damage to human eyes caused by optical radiation has raised more and more attention. In recent years, some corresponding standard agencies have proposed the requirement of classification and grading of such perniciousness.
The test and evaluation of photo biological safety of light source requires the measurement of effective radiance on human retina in order to evaluate the optical radiation safety of the tested light source. The effective radiance of human retina is related to the size of pupil, the sensibility of retinal damage to different wavelengths, spectral characteristics of light sources, duration and other characteristics of human eyes' observation on light sources, and luminous distribution of the surface of light sources.
The existing luminance meters include luminance meter, spectral luminance meter and imaging luminance meter. All of the three types of luminance meter are equipped with imaging optical lens, which will image the luminance signal of the target to the corresponding photoelectric detection instruments. The luminance meter and the spectral luminance meter respectively apply the photoelectric detector with a spectral response of the spectral luminous efficiency function V (λ) and spectroradiometer; the former can only read luminance value, and cannot acquire radiance and other parameters, while the latter can acquire the corresponding effective radiance to the optical damage on human retina through computer software. The imaging luminance meter adopts two-dimensional area array photoelectric detector to measure the distribution of the two-dimensional luminance. Through installation of spectral luminous efficiency function V (λ) optical filter and other special optical filters in front of the two-dimensional detector, two-dimensional luminance or distribution of effective radiance can be acquired, but the precision is less than that of the luminance meter and the spectral luminance meter.
The disadvantages of the existing instruments: aperture of the diagram of the luminance meter is generally large, and the aperture diameter does not relate to the size of human pupil. The measured value of the light sources with narrow light beam distribution, such as LED, would be relatively low, and the hazard of the measured light source would be underestimated. The angle of field of instrument measurement is constant, but when conducting measurements on targets on different distances, focusing will change the effective aperture of the instruments. In addition, the spectral luminance meter can only measure the average luminance and average effective radiance of a certain small area, and it cannot quickly measure the effective radiance of a certain plane. The imaging luminance meter cannot precisely measure the effective radiance of each type of light source.